Coloring photographic images



ture.

Patented Feb. 10, 1942 r I, COLORING PHo'roGRArnm-m -fi I 9 Alan M. Gundelfinger, Los Angeles, calif c Sig or t0v Cinecolor, Incorporated, Los Angeles,

, .Calif., a corporation of Californi a;

1 N0 Drawing. Application December 20, 1938,

- Serial No. 2 16,819- .4 1

r 3 Claims. My invention relates generally to color photography, and has particular reference to the production of metallic-toned images that are both fine-grained and well-definedin appearance. In, many instances and particularly where sound track images are to be colored, it is quite essential that the images be as sharply defined as possible,

' but it, has been found that the conditions. which make for good definition produce, an image'which, is distinctly grainy in appearance.

In motion picture work, where thejimages are f image will beused to denote the or g nal' irnage 'areadefined by. free silverm the first instance andv metallic salt grains subsequently, and the term ,fringe? I will be' used to" denote the diffused outline surrounding 'the image-proper, 'it being understood; t at t temi diffused image wherever used hereinj: means-fan image to greatly magnified by projection on a screen, graininess is very undesirable since it materially detracts from the pleasing appearance of the pic- Furthermore, excessive graininess in sound track images reduces the quality of their sound reproduction.

This problem of graininess versus definition is. alwayspresent when it is desired to tone the'i sound track images and one ormore component picture images simultaneously with the same solution. For example, for many reasons it is.

oftendesirable to use an iron tone to color both the blue component images in a picture and their accompanying sound track in one step, and I have found that when the toning solution is adjusted to' give slightly diffused pictures which I have but little apparent 'grain,the definition of the sound track images is not sufiiciently good to secure faithful reproduction ofjthe sound recorded on the film. Conversely, when the iron toning solution is adjusted to give excellent deflnition and consequently good sound reproduction, the images will exhibit such apparentj'graininess as to be unsatisfactory. j

It is, therefore, the major object of my invention to overcome these obstacles, and to provide a process of toningphotographic' images whereby the images are diffusely colored throughout their image area, and are thus satisfactory for picture projection, which said images also have unusually good definition, and are therefore capable of giving optimum sound reproduction quality.

One suitable method for accomplishing. the object of this invention is disclosed and claimed in the jointapplication of Lyme S. Trimbleland my-, self, Serial No. 246,848, and it is the purpose of;

this invention to provide an additional method of producing a colored photographic image which is satisfactory, both as to diffusion and definition.

color 1throughoutfth e" gelatin in the immediate vicinity of the salt grains formingthc image will [be had." This bleeding "or' di ffusion' of the color within the iinag'efareacolo'rs the gelatin between the salt grains and causesfthe imageto present a more or less un'iform'colored appearance! However, in using such a tone, the color 'also bleeds outwardly frqm the image, and thus' cr'eates a 'lor'entirely-surroundmgtheimage'proper.

In the specification and claim salt infconventionalfmanner; and is then toned with a suitable metallictone, forexarnple an iron toning solution, such as the following:

Ferric ammonium oxalate-; grams 6 Potassium ferricyanide do 6 Ammonium chloride do 10 Hydrochloric acid (conc.)e cc 5 Water to make liter 1 This treatment converts the silver image to a Prussian Blue image whichis generally considered to be ferric ferrocyanide and/or a double salt of ferric ferrocyanide'andan alkali metal ferrocyanide, and in either fcasethe image contains a'silver salt whenfirst formed. In solutions, such as the one above containing a halide, the silver salt in the resulting Prussian Blue image will be a silver halide, but if a toningsolution is used which does not contain a halide, the

silver is in the form of silver'ferrocyanide As previouslymentioned, it is possibleto con- "trol the amount f diffusion and thereby the amount of fringing in the toned [image by controlling the amount of available iron in the toning solution, and I have found that the degree of diffusion varies directly as the ratio of ferricyanide ion concentration to ferric ion concentration in the toning solution. The exact proportions of the various constituents of the toning solution 55 and the precise ratio between ferricyanide and ferric ion concentrations may be varied between comparatively wide limits, depending upon the type of emulsion used. the density of the images, the type of image desired, and the other steps of the general color process. It is to be borne in mind. however, that the toning solution must be adjusted so as to give images which are sufficiently diffused to be satisfactory for picture projectlon which means, of course, that a definite fringe will be produced.

After the image has been toned, the film is preferably washed and is then treated with a solution capable of eliminating the fringe, this treatment being continued until the fringe is substantially eliminated, care being taken, however, to stop the treatment before the color or the structure of the image is materially modified. By this elimination of the fringe, good definition is restored to the image without apparent graininess. In the process of said previously-mentioned copending application, best results are obtained by holding the pH of the second treating solution, therein named, generally between about 6.5 and 7.5, and if the pH in that process is raised much above 8, considerable dimculty is experiencedin controlling the reactions and successfully accomplishing the purposes of the process.

I have now discovered that the fringe can be removed by treating the film with a solution having a relatively high DH value and that the treatment can be controlled within reasonable limits if the reactions mentioned in my said copending application are either absent or kept down to a minimum. In other words, if the Prussian Blue image is treated with a strongly alkaline solution with a pH above 8, and preferably in the vicinity of 9 or 10, direct conversion of substantially all of the Prussian Blue in the fringe and some of the Prussian Blue inthe image properto ferric hydroxide is accomplished. v

The rate of this reaction depends upon the pH of the solution used, or to put it conversely, the pH value chosen depends upon the time allowed for film treatment. The permissible upper limit of the pH depends principally upon the characteristics of the film, since as is well-known,

the ordinary photographic emulsion cannot stand treatment with a solution which is too alkaline. The lower limit of the pH must of course be above 7.0 and from a practical standpoint must be above 8.0, since below that point, the treating,

time is much too long. As mentioned, I prefer a pH between 9 and 10, since with the usual emulsion and blue tone this solution will substantially eliminate the fringe in approximately 3 minutes without materially affecting the image.

Various substances may be employed to furnish the OH ions for the conversion: for example, strongly alkaline salts such as sodium or Dotassium carbonate, tri-sodium phosphate, or the like, or the usual hydroxide of sodium, potassium, ammonia, etc. a

After theconversion to ferric hydroxide has been sufilciently effected as above described, the hydroxide is removed by acid treatment, which fringe may be left in the hydroxide form until the film is immersed in the subsequent treating solution and will be -then removed by the acid therein. i

The ferric ferrocyanide which diffuses out from the agglomerated grains of the image is in a colloidal or highly dispersed state, and is therefore more readily attacked by the OH ions than are the grains themselves. Hence, the amount of ferric ferrocyanide in the fringe is much less than in the image proper, and the preponderance of OH ions in the gelatin of the-fringe is so great that they are but little depleted by reaction with the ferric ferrocyanide which means that the reaction goes substantially to completion. However, in the image proper, due to the greater concentration of the ferric ferrocyanide therein, it greatly preponderates over the OH ions entering that part of the gelatin, and hence the OH ions entering the main body of the image are rapidly depleted before a noticeable amount of the ferric ferrocyanide has been converted; Consequently, if the treatment is stopped when the color has disappeared from the fringe, there still will be no appreciable modification of the color or structure of the image proper, although the overall density will be a trifie lighter.

As previously mentioned; it is highly desirable that no reducing agent be employed in the second treating solution, since the reactions described in said copending application proceed simultaneously with the conversion of the Prussian Blue to ferric hydroxide and the reactions become uncontrollable, there being danger of seriously modifying or impairing the color of the image proper.

I claim as my invention:

1. The method of coloring a metallic photographic image which includes: treating said image with an iron toning solution comprising a soluble ferricyanide and a soluble ferric salt to produce a diffused Prussian Blue image having a fringe; and then treating said image with a solution having a pH above 8.0 until said fringe is @substantially eliminated but the color of said image is not materially modified.

2. The method of coloring a metallic photographic image which includes: treating said image with an iron toning solution comprising a soluble ferricyanide and a soluble ferric salt to produce a diffused Prussian Blue image having a fringe; and then treating said image with a solution whose pH is maintained between approximately 8.0 and 10.5 until said fringe is substanmay take the form of a separate step, or may be solutions used in the color process are acid, the

tially eliminated. but the color of said image is not materially modified.

3. The method of coloring a metallic photographic image which includes: treating said image with an iron toning solution comprising a soluble ferricyanide and a soluble ferric salt to produce a diffused Prussian Blue image having a fringe; and then treating said image with a solution which is sufficiently alkaline to convert ferric ferrocyanide to ferric hydroxide but which will not reduce theferric ions in Prussian Blue to ferrous ions, until said fringe is substantially eliminated but the color of said image is not materially modified.

ALAN M. GUNDELFIN GER. 

